Sometimes the solution can be as bad as the problem. During a ride along the U.S.-Mexico border with Tohono O'odham tribal police, patrol sergeant Ann Miguel was telling me about the problem of cross-border smuggling when the solution came barreling around a corner and nearly ran us off the dirt road. It was a massive border-patrol truck driven by a fresh-faced young agent who offered a half-apologetic wave as he sped on. Miguel sighed. "That's what will get community members upset," she said. "They come flying out of nowhere."

Welcome to the dilemma of being O'odham, as they call themselves. (Tohono means desert; o'odham means people.) The largest cross-border tribe on the U.S.-Mexico line  their U.S. reservation is nearly as big as Connecticut, and 1,500 more members live on the Mexican side  the O'odham are reluctant hosts to a border war they didn't invite. If the influx of federal agents is a mixed blessing for libertarian-minded ranchers elsewhere along the Arizona border, it is causing deeper turmoil for the O'odham and the "sovereign powers of self-government" their constitution invokes. (See pictures of the fence between the United States and Mexico.)

"You never want to see an increase in federal law enforcement on the nation," says Tohono O'odham tribal chairman Ned Norris Jr. But the problem, he says, is simply too big. There are just 47 tribal patrol officers, and one patrol cop can be responsible for up to 600 sq. mi. (1,554 sq km) on a single shift. Meanwhile, heavier enforcement off the reservation has driven smugglers to this remote stretch of the Sonoran Desert; the Baboquivari Trail here is one of the nation's most heavily traveled migrant routes. And some O'odham have been enlisted into working for the cartels. Unemployment is near 50%, says O'odham police chief Joseph Delgado, so when smugglers offer $500 or $1,000 to drive a car an hour or so north through tribal lands, it can be hard to say no. A sting operation in May (the first time tribal police have ever served federal warrants) led to the arrest of eight O'odham for involvement in cocaine trafficking. (See pictures of immigration detention in Arizona.)

The desert confounds efforts to wall off the trouble. On our drive along the border, I saw a half-dozen washes, one as wide as a freeway, where floodwaters had torn down the fencing entirely. When some vehicle barriers went up in 2008 (a controversial process that involved removing ancient O'odham remains), smugglers just put ramps on the Mexican side and jumped their cars over them, like the Dukes of Hazzard. (See pictures of Mexico's drug tunnels.)

As a result, the O'odham government has welcomed more federal agents, and that angers some residents. The tribal government, says O'odham activist Mike Wilson, has "completely surrendered their sovereignty." The newly arrived agents have a lot of power but little knowledge of tribal land and customs, says Ofelia Rivas, founder of O'odham Voice Against the Wall. They don't know to avoid driving on young mesquite, which provides firewood and food when mature. Many sacred sites in the desert lie unmarked and are at similar risk. As for interactions with tribal members, she says, "There's a lot of racial profiling. They look at us and think we're undocumented." Because so many of the migrants, particularly from southern Mexico, are indigenous, many Tohono O'odham feel a particular sympathy for them perhaps not shared by other Arizonans.

It's not clear that the tribal government could resist the federal surge even if it wanted to; the militarization of the U.S.-Mexico border seems an unstoppable force. (Some 1,200 National Guard troops have been deployed to the border this year, nearly half of them in Arizona.) Even if it were possible, leaving the tribe's 75 miles (121 km) of border open and the rest of it closed would invite far greater problems. Still, says Wilson, as long as O'odham continue to be stopped at checkpoints leaving the reservation and asked for ID, they will continue to be wary of their guests in green. "How can the border patrol ask us what we're doing here on our lands?" asks Wilson. "We've been here for 4,000 years. The real question is, What are they doing here?"